1. Field of the Invention
The present invention relates generally to improved methods of preventing well fracture proppant flow-back.
2. Description of the Prior Art
Oil and gas wells are often stimulated by hydraulically fracturing subterranean producing zones penetrated thereby. In such hydraulic fracturing treatments, a viscous fracturing fluid is pumped into the zone to be fractured at a rate and pressure such that one or more fractures are formed and extended in the zone. A solid particulate material for propping the fractures open, commonly referred to as "proppant", is suspended in a portion of the fracturing fluid so that the proppant is deposited in the fractures when the viscous fracturing fluid is caused to revert to a thin fluid and returned to the surface. The proppant functions to prevent the fractures from closing and to form a permeable proppant bed between the fracture faces through which produced fluids can readily flow.
In order to prevent the subsequent flow-back of the proppant as well as subterranean formation particulate solids with fluids produced from the fractured zone, at least a portion of the proppant has heretofore been coated with a hardenable resin composition and consolidated into a hard permeable mass. Typically, the resin composition coated proppant is deposited in the fractures after a large quantity of uncoated proppant material has been deposited therein. That is, the last portion of the proppant deposited in each fracture, referred to in the art as the "tail-in" portion, is coated with a hardenable resin composition. Upon the hardening of the resin composition, the tail-in portion of the proppant is consolidated into a hard permeable mass having a high compressive strength whereby unconsolidated proppant and formation particulate solids are prevented from flowing out of the fractures with produced fluids. While this technique has been successful, the high costs of the hardenable resin composition and the mixing and proppant coating procedures utilized have contributed to making the cost of the fracturing procedure very high.
Thus, there is a continuing need for improved methods of fracturing and placing proppant in subterranean zones whereby the flow-back of the proppant with produced fluids is prevented.